Oubit based systems, devices, and methods for analog processing

ABSTRACT

A system may include first and second qubits that cross one another and a first coupler having a perimeter that encompasses at least a part of the portions of the first and second qubits, the first coupler being operable to ferromagnetically or anti-ferromagnetically couple the first and the second qubits together. A multi-layered computer chip may include a first plurality N of qubits laid out in a first metal layer, a second plurality M of qubits laid out at least partially in a second metal layer that cross each of the qubits of the first plurality of qubits, and a first plurality N times M of coupling devices that at least partially encompasses an area where a respective pair of the qubits from the first and the second plurality of qubits cross each other.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application filed under 35U.S.C. §371 of International Patent Application PCT/US2009/037984,accorded an international filing date of Mar. 23, 2009, which claimsbenefit under 35 U.S.C. 119(e) of U.S. Provisional Patent ApplicationSer. No. 61/039,041, filed Mar. 24, 2008 and entitled “Systems, Methodsand Apparatus for a Superconducting Probe Card”, and claims benefitunder 35 U.S.C. 119(e) of U.S. Provisional Patent Application Ser. No.61/039,710 filed Mar. 26, 2008 and entitled “Systems, Devices, andMethods for Analog Processing.”

BACKGROUND

1. Field

This disclosure generally relates to analog computing and analogprocessors, for example, quantum computing and quantum processors.

2. Description of the Related Art

Approaches to Quantum Computation

There are several general approaches to the design and operation ofquantum computers. One such approach is the “circuit model” of quantumcomputation. In this approach, qubits are acted upon by sequences oflogical gates that are the compiled representation of an algorithm. Muchresearch has been focused on developing qubits with sufficient coherenceto form the basic elements of circuit model quantum computers.

Another approach to quantum computation, involves using the naturalphysical evolution of a system of coupled quantum systems as acomputational system. This approach does not make use of quantum gatesand circuits. Instead, the computational system starts from a knowninitial Hamiltonian with an easily accessible ground state and iscontrollably guided to a final Hamiltonian whose ground state representsthe answer to a problem. This approach does not require long qubitcoherence times and may be more robust than the circuit model. Examplesof this type of approach include adiabatic quantum computation andquantum annealing.

Superconducting Qubits

Superconducting qubits are a type of superconducting quantum device thatcan be included in a superconducting integrated circuit. Superconductingqubits can be separated into several categories depending on thephysical property used to encode information. For example, they may beseparated into charge, flux and phase devices. Charge devices store andmanipulate information in the charge states of the device. Flux devicesstore information in a variable related to the magnetic flux throughsome part of the device. Phase devices store information in a variablerelated to the difference in superconducting phase between two regionsof the phase device. Recently, hybrid devices using two or more ofcharge, flux and phase degrees of freedom have been developed.

Superconducting integrated circuits may include single flux quantum(SFQ) devices. The integration of SFQ devices with superconductingqubits is discussed in U.S. patent application Ser. No. 11/950,276.

BRIEF SUMMARY

A system may be summarized as including a first qubit, a second qubit,wherein a portion of the first qubit crosses the second qubit, and acoupler, having a perimeter, providing a coupling between the firstqubit and the second qubit and proximate to the portion of the firstqubit that crosses the second qubit.

The first qubit may cross the second qubit substantiallyperpendicularly. The perimeter of the coupler may encompass at least apart of the portion of the first qubit that crosses the second qubit.The perimeter of the coupler may encompass a first portions of the firstqubit that does not cross the second qubit and a second portion of thesecond qubit that does not cross the first qubit. The perimeter of thecoupler may include a first arm extending substantially parallel to alength of the first qubit and a second arm extending substantiallyparallel to a length of the second qubit. The first qubit may include afirst qubit loop of superconducting material that is superconductive ata first critical temperature and at least one Josephson junction, thesecond qubit includes a second qubit loop of superconducting materialthat is superconductive at a second critical temperature and at leastone Josephson junction, and the coupler includes a coupling loop ofsuperconducting material that is superconductive at a third criticaltemperature. The coupling loop may be interrupted by at least oneJosephson junction. The coupler may be on a separate layer from thefirst and the second qubits. The coupler may be on a same layer as oneof the first or the second qubits. The first coupler may be operable toat least one of ferromagnetically, anti-ferromagnetically andtransversely couple the first qubit and the second qubit.

A multi-layered computer chip may be summarized as a first plurality Nof qubits laid out at least partially in a first metal layer, a secondplurality M of qubits laid out at least partially in a second metallayer; each of the qubits of the second plurality of qubits cross eachof the qubits of the first plurality of qubits, and a first plurality Ntimes M of coupling devices, each of the coupling devices proximate towhere a respective pair of the qubits from the first and the secondplurality of qubits cross each other. At least of the coupling devicesmay include a first arm extending substantially parallel to a length ofa qubit of the first plurality of N qubits and a second arm extendingsubstantially parallel to a length a second qubit of the secondplurality of M qubits. The plurality of coupling devices may be laid outat least partially in the second metal layer. M may be equal to N. Themulti-layered computer chip may include a metal shielding layerpositioned to reduce magnetic noise around the qubits and the couplers.The second plurality of qubits may be laid out in both the second metallayer and the first metal layer and a plurality of vias may providerespective current paths between the second and the first metal layers.The plurality of coupling devices may be laid out in both the secondmetal layer and the first metal layer and a plurality of vias mayprovide respective current paths between the second and the first metallayers. The qubits of the first plurality of qubits may be arrangedparallel to one another, the qubits of the second plurality of qubitsmay be arranged parallel to one another, and the qubits of the secondplurality of qubits may be arranged perpendicularly with respect to thequbits of the first plurality of qubits. The qubits of the firstplurality of qubits may be arranged in a consecutive order from a firstto an n^(th) qubit, the qubits of the second plurality of qubits arearranged in a consecutive order from a first qubit to an m^(th) qubit,the first qubit of the first plurality of qubits is ferromagneticallycoupled to the first qubit of the second plurality of qubits, a secondqubit of the first plurality of qubits is ferromagnetically coupled to asecond qubit of the second plurality of qubits, a third qubit of thefirst plurality of qubits is ferromagnetically coupled to a third qubitof the second plurality of qubits, a fourth qubit of the first pluralityof qubits is ferromagnetically coupled to a fourth qubit of the secondplurality of qubits, the first qubit of the first plurality of qubits iscontrollably coupleable to each of the second, the third and the fourthqubits of the second plurality of qubits, the second qubit of the firstplurality of qubits is controllably coupleable to each of the first, thethird and the fourth qubits of the second plurality of qubits, the thirdqubit of the first plurality of qubits is controllably coupleable toeach of the first, the second, and the fourth qubits of the secondplurality of qubits, and the fourth qubit of the first plurality ofqubits is controllably coupleable to each of the first, the second, andthe third qubits of the second plurality of qubits to form a first K₄block. The multi-layered computer chip may include a third plurality Iof qubits laid out in a first metal layer, a fourth plurality J ofqubits laid out at least partially in a second metal layer; each of thequbits of the second plurality of qubits cross each of the qubits of thefirst plurality of qubits, a fifth plurality K of qubits laid out in afirst metal layer, a sixth plurality L of qubits laid out at leastpartially in a second metal layer; each of the qubits of the secondplurality of qubits cross each of the qubits of the first plurality ofqubits, a second plurality I times J of coupling devices, each of thecoupling devices of the second plurality of coupling devices at leastpartially encompassing an area where a respective pair of the qubitsfrom the third and the fourth plurality of qubits cross each other,wherein the qubits of the third plurality of qubits are arranged in aconsecutive order from a first to an nth qubit, the qubits of the fourthplurality of qubits are arranged in a consecutive order from a firstqubit to an nth qubit, the first qubit of the third plurality of qubitsis controllably coupleable to each of the first, the second, the thirdand the fourth qubits of the fourth plurality of qubits, the secondqubit of the third plurality of qubits is controllably coupleable toeach of the first, the second, the third and the fourth qubits of thefourth plurality of qubits, the third qubit of the third plurality ofqubits is controllably coupleable to each of the first, the second, thethird, and the fourth qubits of the fourth plurality of qubits, and thefourth qubit of the third plurality of qubits is controllably coupleableto each of the first, the second, the third, and the fourth qubits ofthe fourth plurality of qubits to form a first bipartite block, and athird plurality K times L of coupling devices, each of the couplingdevices of the second plurality of coupling devices at least partiallyencompassing an area where a respective pair of the qubits from thethird and the fourth plurality of qubits cross each other, wherein thequbits of the fifth plurality of qubits are arranged in a consecutiveorder from a first to an nth qubit, the qubits of the sixth plurality ofqubits are arranged in a consecutive order from a first qubit to an nthqubit, the first qubit of the fifth plurality of qubits isferromagnetically coupled to the first qubit of the sixth plurality ofqubits, a second qubit of the fifth plurality of qubits isferromagnetically coupled to a second qubit of the sixth plurality ofqubits, a third qubit of the fifth plurality of qubits isferromagnetically coupled to a third qubit of the sixth plurality ofqubits, a fourth qubit of the fifth plurality of qubits isferromagnetically coupled to a fourth qubit of the sixth plurality ofqubits, the first qubit of the fifth plurality of qubits is controllablycoupleable to each of the second, the third and the fourth qubits of thesixth plurality of qubits, the second qubit of the fifth plurality ofqubits is controllably coupleable to each of the first, the third andthe fourth qubits of the sixth plurality of qubits, the third qubit ofthe fifth plurality of qubits is controllably coupleable to each of thefirst, the second, and the fourth qubits of the sixth plurality ofqubits, and the fourth qubit of the fifth plurality of qubits iscontrollably coupleable to each of the first, the second, and the thirdqubits of the sixth plurality of qubits to form a second K₄ block, andwherein the qubits of the third plurality of qubits areferromagnetically coupled with respective ones of the qubits of thefirst plurality of qubits and wherein the qubits from the fourthplurality of qubits are ferromagnetically coupled with respective onesof the qubits of the sixth plurality of qubits to form a first K₈ block.The multi-layered computer chip may include an additional plurality ofqubits and an additional plurality of couplers configured to form asecond K₈ block, wherein at least one qubit from the first K₈ block iscontrollably coupled to at least one qubit from the second K₈ block. Atleast one of the couplers may be a corner coupler that is operable tocouple at least one qubit from the first K₄ block to a correspondingrespective qubit from the either the fifth or the sixth plurality ofqubits. The multi-layered computer chip may include a superconductingprobe card to establish an interface between the multi-layered computerchip and a digital computer, the superconducting probe including aprinted circuit board including a dielectric medium that carries atleast a first conductive trace, wherein the first conductive trace isformed by a material that is superconducting below a criticaltemperature, and at least a first conductive needle that is at leastpartially formed by a material that is superconducting below a criticaltemperature, wherein a first end of the first conductive needle iscommunicably coupled to the first conductive trace on the printedcircuit board and a second end of the first conductive needle is taperedto form a point.

A superconducting probe card may be summarized as including a printedcircuit board including a dielectric medium that carries at least afirst conductive trace, wherein the first conductive trace is formed bya material that is superconducting below a critical temperature; and atleast a first conductive needle that is at least partially formed by amaterial that is superconducting below a critical temperature, wherein afirst end of the first conductive needle is communicably coupled to thefirst conductive trace on the printed circuit board and a second end ofthe first conductive needle is tapered to form a point; wherein thecritical temperature of the first conductive trace and the criticaltemperature of the first conductive needle are both approximately equalto or greater than an operating temperature of the superconducting probecard. The printed circuit board may carry at least a first contact padthat is formed by a material that is superconducting below a criticaltemperature, and the first contact pad may be superconductinglycommunicably coupled to the first conductive trace, such that thecommunicable coupling between the first conductive trace and the firstconductive needle is realized through the first contact pad. The firstend of the first conductive needle may be coated with a solderablematerial that is superconducting below a critical temperature, such thatthe first end of the first conductive needle may be communicably coupledto the first contact pad on the printed circuit board by asuperconducting solder connection. The solderable material may includezinc. The solderable material may include at least one of tin and lead.The first conductive needle may be formed of an alloy oftungsten-rhenium where the proportion of rhenium in the alloy is greaterthan 4% and less than 50%. The proportion of rhenium in the alloy may bein the range of 10%-40%. The proportion of rhenium in the alloy may beapproximately 26%. The printed circuit board may include a hole throughthe dielectric medium and the first conductive needle may include a bendin its length such that the point at the second end of the firstconductive needle extends through the hole. The second end of the firstconductive needle may be superconductingly communicably coupled to asuperconducting device. The superconducting device may include asuperconducting integrated circuit. The superconducting device mayinclude a superconducting processor. The superconducting processor mayinclude a superconducting quantum processor. The superconducting quantumprocessor may include at least one device selected from the groupconsisting of: a superconducting flux qubit, a superconducting phasequbit, a superconducting charge qubit, a superconducting hybrid qubit, asuperconducting coupling device, and a superconducting readout device.

The superconducting probe card may further include a plurality ofadditional conductive traces carried by the dielectric medium, whereineach of the additional conductive traces is formed by a material that issuperconducting below a critical temperature; and a plurality ofadditional conductive needles, wherein each of the additional conductiveneedles is formed by a material that is superconducting below a criticaltemperature and wherein a respective first end of each of the additionalconductive needles is communicably coupled to at least one of theplurality of additional conductive traces and a respective second end ofeach of the additional conductive needles is tapered to from a point;wherein the critical temperature of the plurality of additionalconductive traces and the critical temperature of the plurality ofadditional conductive needles are both approximately equal to or greaterthan the operating temperature of the superconducting probe card. Theprinted circuit board may carry a plurality of contact pads, whereineach contact pad is formed by a material that is superconducting below acritical temperature, and wherein each contact pad is superconductinglycommunicably coupled to a respective one of the conductive traces suchthat each communicable coupling between a conductive trace and at leastone conductive needle is realized through a respective contact pad. Thefirst end of each conductive needle may be coated with a solderablematerial that is superconducting below a critical temperature, and thefirst end of each conductive needle may be communicably coupled to atleast one contact pad on the printed circuit board by a superconductingsolder connection. The printed circuit board may include a hole throughthe dielectric medium and each conductive needle includes a bend in itslength such that the point at the second end of each conductive needleextends through the hole. The second end of each conductive needle maybe superconductingly communicably coupled to at least one contact padcarried by a superconducting device. The dielectric medium, the firstconductive trace, and the first conductive needle may each be formed bymaterials that are substantially non-magnetic. The superconducting probecard may include at least two conductive needles that are bothcommunicably coupled to the same conductive trace on the printed circuitboard. The first conductive needle may include a plated layer of thematerial that is superconducting below the critical temperature.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn are not intendedto convey any information regarding the actual shape of the particularelements, and have been solely selected for ease of recognition in thedrawings.

FIGS. 1A and 1B are functional diagrams showing systems for solvingcomputational problems according to one illustrative embodiment.

FIG. 2A is a diagram showing systems for solving computational problemsaccording to an illustrative embodiment.

FIG. 2B is a diagram showing systems for solving computational problemsaccording to an illustrative embodiment.

FIG. 3 is a diagram of a source graph.

FIG. 4 is a diagram of a source graph.

FIG. 5 is a diagram showing systems for solving computational problemsaccording to an additional illustrative embodiment.

FIG. 6 is a diagram showing systems for solving computational problemsaccording to a further illustrative embodiment.

FIG. 7 is a top plan view of a superconducting probe card according toone illustrated embodiment.

FIG. 8A is a side elevational view of a superconducting needle for usein a superconducting probe card, according to one illustratedembodiment.

FIG. 8B is a side elevational view of a superconducting needle includinga bend in its length according to one illustrated embodiment, for use ina superconducting probe card.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedembodiments. However, one skilled in the relevant art will recognizethat embodiments may be practiced without one or more of these specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures associated with quantum processors,qubits, couplers, controller, readout devices and/or interfaces have notbeen shown or described in detail to avoid unnecessarily obscuringdescriptions of the embodiments.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

The headings and Abstract of the Disclosure provided herein are forconvenience only and do not interpret the scope or meaning of theembodiments.

Systems for Solving Computational Problems

FIG. 1A shows an exemplary problem-solving system 100. Problem-solvingsystem 100 may include a computer 102 and an analog processor 150. Ananalog processor is a processor that employs the fundamental propertiesof a physical system to find the solution to a computation problem. Incontrast to a digital processor, which requires an algorithm for findingthe solution followed by the execution of each step in the algorithmaccording to Boolean methods, analog processors do not involve Booleanmethods.

Computer 102 may include one or more controllers such as microprocessor110, non-volatile storage controller 125, digital signal processor (DSP)(not shown), analog processor 150, and the like. Computer 102 mayfurther include one or more memories 126 coupled to controllers 110,125, 150 by one or more busses 106. Examples of the one or more memoriesinclude a system memory 126, such as high speed random-access memory(RAM), for storing system control programs (e.g., operating system 128,application programs loaded from main non-volatile storage unit 120,data, and the like), and a read-only memory (ROM). Computer 102 may alsoinclude a main non-volatile storage unit 120, a user interface 114, anetwork interface card (NIC) 124, communication circuitry, a networkconnection 118, and the like. NIC 124, communication circuitry, networkconnection 118 and the like may provide one or more communication paths,for example allowing the system to communicate with one or more externaldevices (e.g., external computing systems, server computing systems,memories, etc). User interface 114 may also include one or more inputdevices 116 including a display 112, a mouse, a keyboard, and otherperipheral devices.

Computer 102 may include an operating system 128 for handling varioussystem services, such as file services, and for performing hardwaredependent tasks. Examples of operating system 128 include UNIX, WindowsNT, Windows XP, DOS, LINUX, VMX, and the like. Alternatively, nooperating system 128 may be present and instructions may be executed,for example, in a daisy chain manner. In an embodiment, computer 102 maytake the form of a digital computer. In another embodiment, analogprocessor 150 may be in communication with computer 102.

Analog processor 150 may take the form of quantum processor 150 a shownin FIG. 1B, including a plurality of qubits 172 a-172 d (only fourcalled out in figure) forming an interconnected topology, a plurality ofcoupling devices 174 a-174 d (only four called out in figure), a readoutdevice 160, a qubit control system 162, and a coupling device controlsystem 164. Quantum processor 150 a may include at least two qubits 172a, 172 b, at least one coupling device 174 a, and at least one localbias device.

Interconnected topology of qubits 172, collectively, serves as the basisfor performing quantum computation, and may take the form ofsuperconducting qubits. Examples of qubits include quantum particles,atoms, electrons, photons, ions, and the like. Typical superconductingqubits, for example, have the advantage of scalability and are generallyclassified depending on the physical properties used to encodeinformation including, for example, charge and phase devices, phase orflux devices, hybrid devices, and the like.

Quantum processor 150 a may further include a readout device 160.Readout device 160 may include a plurality of dc-SQUID magnetometers,each inductively connected to a different qubit within interconnectedtopology 172. NIC 124 may be configured to receive a voltage or currentfrom readout device 160. The dc-SQUID magnetometers including a loop ofsuperconducting material interrupted by at least one Josephson junctionsare well known in the art.

Qubit control system 162 may include one or more controllers forinterconnected topology of qubits 172. Coupling device control system164 may include one or more coupling controllers for the couplingdevices, collectively 174. Each respective coupling controller incoupling device control system 164 may be configured to tune thecoupling strength of a corresponding coupling device 174 a-174 d fromzero to a maximum value. Coupling devices 174 may be tuned, for example,to provide ferromagnetic or anti-ferromagnetic coupling between qubits172.

Problem-solving system 100 may further include a number of programs anddata structures. Typically, some or all of the data structures andprograms may be stored in one or more memories including system memory126, random-access memory 111, read-only memory 113, and the like. Suchmay include storing information regarding at least one of: a couplingstate corresponding to at least one of the controllable coupling devicesor an initial basis state corresponding to at least one of the quantumdevices. Likewise these programs and data structures or information maybe processed using one or more microprocessors 110, analog processors150, and the like. For ease of presenting the various features andadvantages of the present systems, devices, and methods, however, suchdata structures, and programs are drawn as components of system memory126. It will be appreciated, however, that at any given time theprograms and data structures illustrated in system memory 126 or otherinformation (e.g., information regarding at least one of: a couplingstate corresponding to at least one of the controllable coupling devicesor an initial basis state corresponding to at least one of the quantumdevices) may be stored, for example, in non-volatile storage unit 120.In some embodiments, some or all of the data structures and programs maybe stored on one or more remote computers not illustrated in FIG. 1A,provided that the one or more remote computers are addressable bycomputer 102, i.e., that there is some communication measure between theremote computer and computer 102 such that data can be exchanged amongcomputers over, for example, a data network (e.g., the Internet, aserial connection, a parallel connection, Ethernet, and the like) usinga communication protocol (e.g., FTP, telnet, SSH, IP, and the like). Insome other embodiments, some or all of the data structures and programsmay be redundantly stored and/or processed on one or more remotecomputers (not shown), provided that the one or more remote computersare addressable by computer 102.

Problem-solving system 100 may further include a receiver 130, apre-processing manager 132, an analog processor interface 134 such as aquantum processor interface 134 a, and a post-processing manager 136.Receiver 130 may be configured to receive problems to be solved on theanalog processor 150. Receiver 130 may further be configured to send aresponse to a computational problem processing request.

In an embodiment, receiver 130, pre-processing manager 132, quantumprocessor interface 134 a and post-processing manager 136 are allimplemented in one or more digital computing systems. In anotherembodiment, at least one of receiver 130, pre-processing manager 132,quantum processor interface 134 a, and post-processing manager 136 maybe in a location remote from quantum processor 150 a.

Microprocessor 110 may be configured to determine an estimate forproducing one or more solutions to the computational problem processingrequests based in part on a comparison to problems of like complexity.

Analog processor 150 may be operable to produce one or more solutions tocomputational problems identified by the computational problemprocessing requests. In some embodiments, analog processor 150 may beoperable to obtain one or more solutions to the computational problemsvia a physical evolution of the analog processor. In another embodiment,problem-solving system 100 may include additional analog processors 150operable to redundantly co-process one or more solutions tocomputational problems identified by the computational problemprocessing requests.

A computational problem may be received by the problem-solving system100 via a telephone modem, a wireless modem, a local area networkconnection, a wide area network connection, a portable digital datadevice, and the like. The information received by receiver 130 mayinclude initial values of couplings between qubits 172, local bias ofqubits 172, run-time control parameters, and the like. Alternatively,the information received by receiver 130 may include a graph thatrepresents a computational problem, macro-language instructions, such asAMPL, that define a computational problem, and the like.

Receiver 130 may be operable to provide instructions for scheduling acomputation, as well as acquiring the solution to the problem. In anembodiment, a solution of the computation is collected as an output fromquantum processor 150 a. In another embodiment, receiver 130 mayoptionally include a graphical user interface (GUI), Command LineInterfaces (CLI), Text User Interface (TUI), and the like. In anotherembodiment, receiver 130 is operable to receive graphicalrepresentations of the computational problem.

Problem-solving system 100 may further include one or morecommunications links, such as, for example, a network connection 118,for sending and receiving data among at least two of receiver 130,pre-processing manager 132, quantum processor interface 134 a, quantumprocessor 150 a, and post-processing manager 136. The communicationslink may further include an encryption interface (not shown).

Pre-processing manager 132 may be configured to receive thecomputational problem processing request from receiver 130, and convertthe computational problem processing requests into a first series ofinstructions. Pre-processing manager 132 may further be configured fordetermining a first Hamiltonian. In an embodiment, pre-processingmanager 132 is configured for mapping a computational problem into aproblem of an equivalent complexity class. In another embodiment,pre-processing manager 132 includes logic to map the computationalproblem into at least one of a problem of equivalent, greater or lessercomplexity class. In an embodiment, the logic to map the computationalproblem onto analog processor 150 includes instructions for mapping thecomputational problem onto a topological representation and embeddingthe topological representation onto analog processor 150. In anembodiment, the topological representation is in a form of at least oneof a planar graph or a non-planar graph. In another embodiment, thetopological representation is a graph in the form of a plurality ofvertices, and one or more edges. In another embodiment, the topologicalrepresentation is an interconnected graph of the same structure had bythe interconnected topology of qubits.

In another embodiment, pre-processing manager 132 is configured formapping a computational problem onto analog processor 150, for example,quantum processor 150 a. Mapping a computational problem onto analogprocessor 150 may include, for example, mapping the computationalproblem onto a graph and embedding the graph onto analog processor 150.

Quantum processor interface 134 a may be operable to receive a firstseries of instructions from pre-processing manager 132. Quantumprocessor 150 a may be configured to receive a second series ofinstructions from quantum processor interface 134 a, and obtain asolution to the computational problem processing request by a physicalevolution of the analog processor. Post-processing manager 136 may beconfigured to convert the solution into a post-processed solution.

Pre-processing manager 132 may include a mapper interface configured tomap a computational problem to be solved into a corresponding problemdescription that is solvable by analog processor 150. The mapperinterface may be configured to map problems from one graphicalrepresentation into a target graphical representation required for aspecific configuration of analog processor 150. In an embodiment, thetarget graphical representation may include an interconnected topology,analog processor 150 may take the form of a quantum processor 150 a thatmay include a lattice of qubits 172 and coupling devices 174, and eachcoupling device 174 may be configured to couple two qubits 172 together.

The mapper interface may be configured to map some NP problems (e.g., amathematical problem such as Maximum Independent Set, Max Clique, MaxCut or k-SAT, or a problem such as an integer programming problem, aconstraint optimization problem, a factoring problem, a predictionmodeling problem, an operations research problem, a financial portfolioselection problem, a scheduling problem, a supply management problem, acircuit design problem, a travel route optimization problem, a businessprocess simulation problem, an ecological habitat simulation problem, aprotein folding simulation problem, a molecular ground state simulationproblem or a quantum system simulation problem, and the like) intoanother NP problem, such as the Ising Spin Glass problem or otherproblems already mentioned.

Once the target graphical representation needed to solve a desiredproblem has been mapped by the mapper interface, quantum processorinterface 134 a is used to set up the coupling values and local biasvalues for coupling devices 174 and interconnected qubits 172 in orderto map the representation onto quantum processor 150 a. In anembodiment, three discrete program modules may provide the functions ofquantum processor interface 134 a: an initialization module 140, anevolution module 142, and an output module 144.

Initialization module 140 may be configured to determine the appropriatevalues of coupling J_(ij) for coupling devices 174 and values of localbias h_(i) for interconnected qubits 172. Initialization module 140 maybe configured to convert aspects of a problem definition into physicalvalues, such as coupling strength values and qubit bias values, whichcan be programmed into quantum processor 150 a. Initialization module140 may then be configured to send the appropriate signals along one ormore internal buses 106 into NIC 124. NIC 124, in turn, may beconfigured to send such commands to qubit control system 162 andcoupling device control system 164.

For any given problem, evolution module 142 may be configured todetermine the appropriate values, at each point in time for the durationof the computation, of coupling J_(ij) for coupling devices 174 andvalues of local bias h_(i) for interconnected qubits 172 to fulfill somepredetermined evolution schedule (i.e. the schedule for how theevolution is to take place). Once determined, the appropriate couplingdevice values and local bias values for an evolution schedule are sentas signals, via one or more buses 106, to NIC 124. NIC 124, in turn, isconfigured to send such commands to quantum device control system 162and coupling device control system 164.

The computation of analog processor 150 may be configured to operate as,for example, an adiabatic evolution or an annealing evolution. Anadiabatic evolution is the evolution used in adiabatic analog computing,and evolution module 142 may be configured to evolve the state of theanalog processor 150 in accordance with the evolution used in adiabaticquantum computation. See, e.g., U.S. Patent Publication Nos.2005-0256007, 2005-0250651, and 2005-0224784 each titled “AdiabaticQuantum Computation with Superconducting Qubits.” Annealing is anotherform of evolution applicable to some analog processors 150, andevolution module 142 may be configured to evolve the state of analogprocessor 150 in accordance with annealing evolution.

Quantum processor 150 a may be configured to solve a quantum problembased on signals provided by initialization module 140 and evolutionmodule 142. Once the problem has been solved, the solution to theproblem may be measured from the states of interconnected qubits 172 byreadout device 160. Output module 144 may be configured in conjunctionwith readout device 160 to read this solution.

System memory 126 may further include a driver module 146 configured tooutput signals to analog processor 150. NIC 124 may be configured tointerface with interconnected qubits 172 and coupling devices 174,either directly or through readout device 160, qubit control system 162,and/or coupling device control system 164. Alternatively, NIC 124 mayinclude software and/or hardware that translates commands from drivermodule 146 into signals (e.g., voltages, currents) that are directlyapplied to interconnected qubits 172 and coupling devices 174. In anembodiment, NIC 124 may include software and/or hardware for translatingsignals (representing a solution to a problem or some other form offeedback) from interconnected qubits 172 and the coupling devices 174such that output module 144 can interpret them. In some embodiments,initialization module 140, evolution module 142, and/or output module144 may communicate with driver module 146, rather than directly withNIC 124, to send and receive signals from analog processor 150.

The functionality of NIC 124 can be divided into two classes: dataacquisition and control. Different types of chips may be used to handleeach discrete functional class. Data acquisition is used to measurephysical properties of interconnected qubits 172 after quantum processor150 a has completed a computation. Such data can be measured using anynumber of customized or commercially available data acquisitionmicro-controllers including data acquisition cards manufactured by ElanDigital Systems (Fareham, UK) including the AD132, AD136, MF232, MF236,AD142, AD218, CF241 cards, and the like. Alternatively, a single type ofmicroprocessor, such as the Elan D403C or D480C, may handle dataacquisition and control. There may be multiple NICs 124 in order toprovide sufficient control over interconnected qubits 172 and couplingdevices 174 and in order to measure the results of a quantum computationon quantum processor 150 a.

Computer 102 may further be configured for receiving a computationalproblem and transmitting the solution of a computational problemprocessed by analog processor 150 to another system, such as via atelephone modem, a wireless modem, a local area network (LAN)connection, a wide area network (WAN) connection, a portable digitaldata device, and the like. Computer 102 may be configured to generate acarrier wave embodying a data signal, with the solution to thecomputational problem processed by analog processor 150 embeddedtherein.

Analog processor 150 may be in the form of a superconducting quantumcomputer, examples of which include qubit registers, readout devices,and ancillary devices. Superconducting quantum computers normally areoperated at milliKelvin temperatures and often are operated in adilution refrigerator. An example of a dilution refrigerator is theLeiden Cryogenics B.V. MNK 126 series (Galgewater No. 21, 2311 VZLeiden, The Netherlands). All or part of the components of quantumprocessor 150 a may be housed in a dilution refrigerator. For example,qubit control system 162 and coupling device control system 164 may behoused outside a dilution refrigerator with the remaining components ofquantum processor 150 a being housed inside a dilution refrigerator.

Receiver 130, quantum processor interface 134 a, and driver module 146,or any combination thereof, may be implemented via existing softwarepackages. Suitable software packages include, for example, MATLAB (TheMathWorks, Natick, Mass.), LabVIEW (National Instruments, Austin, Tex.),Maple (Waterloo Maple Inc., Waterloo, Ontario, Canada.), Mathematica(Wolfram Research, Inc., Champaign, Ill.), and the like.

In an embodiment, receiver 130 may be configured to receive acomputational problem processing request, and to provide identityinformation indicative of an entity responsible (e.g., financiallyresponsible) for the received computational problem processing request.

In an embodiment, the present systems, devices, and methods may beimplemented as a computer program product that includes a computerprogram mechanism embedded in a computer readable storage medium. Forexample, the computer program product may include aspects of the quantumprocessor interface 134 a, operating system 128, receiver 130,pre-processing manager 132, post-processing manager 136 and the like.Aspects of the various interfaces, managers, and modules, may be storedon a CD-ROM, DVD, magnetic disk storage product, any other computerreadable data or program storage product, and may also be distributedelectronically, via the Internet or otherwise, by transmission of acomputer data signal (in which the software modules are embedded)embodied in a carrier wave, and the like.

In an embodiment, the problem-solving system 100 may include amicroprocessor 110, a receiver 130, a pre-processing manager 136 and aquantum processor interface 134 a. Receiver 130 may be configured toreceive a computational problem processing request and provide identityinformation indicative of an entity responsible for the receivedcomputational problem processing request. Quantum processor interface134 a may be configured to convert the computational problem processingrequest into a series of instructions receivable by quantum processor150 a, to obtain a solution to the computational problem processingrequest, and/or to send a solution to the computational problem.

In other embodiments, problem-solving system 100 may include additionalprocessors 110 configured to store execution data including processingvariables, solution parameters, simulation trajectories, checkpoints,and the like throughout the processing of a computational problemprocessing request. For example, by storing execution data atpredetermined times or after predetermined acts, it may be possible toreturn problem-solving system 100 to a predetermined point orcheckpoint. Storing the execution data at predetermined times mayinclude, for example, storing the execution data at regular intervals oraccording to a user-determined schedule.

In an embodiment, in the event that problem-solving system 100experiences a power loss, and/or an application or the operating systemstops performing its expected function and/or portions of an applicationor the operating system stop responding to other parts of the system,stored processing variables, solution parameters, simulationtrajectories, and/or checkpoints, and the like may be used to returnproblem-solving system 100 to a predetermined point or checkpoint.

Interconnected Topology

A complete graph with n vertices (denoted K_(n)) is a graph with nvertices in which each vertex is connected to each of the others (withone edge between each pair of vertices). In some embodiments the edgebetween each pair of vertices may be connected, empty or weighted.

FIG. 2A shows a topology 200 a which may include qubits 210 a-d(collectively 210) and qubits 220 a-d (collectively 220). Qubits 210 arelaid out vertically in FIG. 2A and qubits 220 are laid out horizontallyin FIG. 2A. A person of skill in the art will appreciate that while fourqubits are illustrated both horizontally and vertically, this number isarbitrary and embodiments may comprise more or less than four qubits.Qubits 210, 220 may be superconducting qubits. Crosstalk between qubits210 and qubits 220 may not exist in some embodiments of the presentsystems and methods. For crosstalk, or the unintended coupling ofqubits, to exist, two current carrying wires from two respective qubitsmust run parallel in some manner to allow flux from current within afirst wire to induce a current to flow in a second wire. Since qubits210 and qubits 220 run perpendicular to one another, crosstalk betweenqubits 210 and qubits 220 may be limited. Hence, while qubits 210 andqubits 220 may be proximate to each other, no coupling will existsbetween pairs of qubits from qubits 210 and qubit 220 if not by througha third structure. Each qubit 210 a-d may be a respective loop ofsuperconducting material 212 a-d interrupted by at least one respectiveJosephson junction 215 a-d. Each qubit 220 a-d may be a respective loopof superconducting material 222 a-d interrupted by at least onerespective Josephson junction 225 a-d. Couplers 230 a-230 p(collectively 230) couple qubits 210, 220. Each qubit 210 a-d is coupledto each qubit 220 a-d through four respective couplers from couplers 230in a region proximate to where a portion of each qubit 210 a-d crosses aportion of qubit 220 a-d. Each coupler 230 a-p may be a respective loopof superconducting material wherein the loop or superconducting materialmay define a perimeter to a coupling region. Each coupler 230 a-p may bea respective loop of superconducting material interrupted by at leastone respective Josephson junction wherein the loop or superconductingmaterial may define a perimeter to a coupling region wherein couplingoccurs along the perimeter by having a current carrying wire, such asloop of superconducting material 212 a-d, 222 a-d, run parallel in somemanner to coupler 230 a-p to allow flux from current within loop ofsuperconducting material 212 a-d, 222 a-d to induce a current to flow ina coupler 230 a-p and vice versa. Couplers 230 may be tunable in thatthe coupling couplers 230 create between two respective qubits 210, 220can be changed during the operation of an analog processor. The couplingmay change during computation. The coupling may change betweencomputations to embed a problem into the analog processor.

FIG. 2B shows a topology 200B which may include qubits 210 a-d(collectively 210) and qubits 220 a-d (collectively 220). Qubits 210 arelaid out vertically in FIG. 2B and qubits 220 are laid out horizontallyin FIG. 2B. A person of skill in the art will appreciate that while fourqubits are illustrated both horizontally and vertically, this number isarbitrary and embodiments may comprise more or less than four qubits.Qubits 210, 220 may be superconducting qubits. Crosstalk between qubits210 and qubits 220 may not exist in some embodiments of the presentsystems and methods. For crosstalk, or the unintended coupling ofqubits, to exist, two current carrying wires from two respective qubitsmust run parallel in some manner to allow flux from current within afirst wire to induce a current to flow in a second wire. Since qubits210 and qubits 220 run perpendicular to one another, crosstalk betweenqubits 210 and qubits 220 may be limited. Hence, while qubits 210 andqubits 220 may be proximate to each other, no coupling will existsbetween pairs of qubits from qubits 210 and qubit 220 if not by througha third structure. Each qubit 210 a-d may be a respective loop ofsuperconducting material 212 a-d interrupted by at least one respectiveJosephson junction 215 a-d. Each qubit 220 a-d may be a respective loopof superconducting material 222 a-d interrupted by at least onerespective Josephson junction 225 a-d. Couplers 240 a-240 p(collectively 240) couple qubits 210, 220. Each qubit 210 a-d is coupledto each qubit 220 a-d through four respective couplers from couplers 240in a region proximate to where a portion of each qubit 210 a-d crosses aportion of qubit 220 a-d. Each coupler 240 a-p may be a respective loopof superconducting material wherein the loop or superconducting materialmay define a perimeter to a coupling region, the perimeter having twoarms: a first arm extending substantially parallel to a respective qubitof qubits 210, and a second arm extending substantially parallel to arespective qubit of qubits 220. The perimeter may or may not encompass apart of the portions a respective pair of qubits 210 and qubits 220 thatcross one another. Each coupler 240 a-p may be a respective loop ofsuperconducting material interrupted by at least one respectiveJosephson junction wherein the loop or superconducting material maydefine a perimeter to a coupling region wherein coupling occurs alongthe perimeter by having a current carrying wire, such as loop ofsuperconducting material 212 a-d, 222 a-d, run parallel in some mannerto coupler 230 a-p to allow flux from current within loop ofsuperconducting material 212 a-d, 222 a-d to induce a current to flow ina coupler 230 a-p and vice versa. Couplers 240 may be tunable in thatthe coupling couplers 240 create between two respective qubits 210, 220can be changed during the operation of an analog processor. The couplingmay change during computation. The coupling may change betweencomputations to embed a problem into the analog processor.

Couplers 230, 240 may mark the vertices of a grid defined by the qubits210 and 220 and exist where qubits 210, 220 are proximate to each otherthereby facilitating efficient coupling. By ferromagnetically couplingalong diagonal couplers 230 a, 230 f, 230 k, 230 p or couplers 240 a,240 f, 240 k, 240 p a fully connected K₄ graph 300, such as is shown inFIG. 3, can be embedded into topology 200 a, 200 b. In one embodiment,node 301 may be embedded into qubits 210 a, 220 a where coupler 230 a,240 a ferromagnetically couples qubits 210 a, 220 a together such thatthe state of qubit 210 a is the same state as the state of qubit 220 a.Node 302 may be embedded into qubits 210 b, 220 b where coupler 230 f,240 f ferromagnetically couples qubits 210 b, 220 b together such thatthe state of qubit 210 b is the same state as the state of qubit 220 b.Node 303 may be embedded into qubits 210 c, 220 c where coupler 230 k,240 k ferromagnetically couples qubits 210 c, 220 c together such thatthe state of qubit 210 c is the same state as the state of qubit 220 c.Node 304 may be embedded into qubits 210 d, 220 d where coupler 230 p,240 p ferromagnetically couples qubits 210 d, 220 d together such thatthe state of qubit 210 d is the same state as the state of qubit 220 d.Edge 312 may be embedded into coupler 230 b, 230 e or 240 b, 240 e. Edge313 may be embedded into coupler 230 c, 230 i or 240 c, 240 i. Edge 314may be embedded into coupler 230 d, 230 m or 240 d, 240 m. Edge 323 maybe embedded into coupler 230 g, 230 j or 240 g, 240 j. Edge 324 may beembedded into coupler 230 h, 230 n or 240 h, 240 n. Edge 334 may beembedded into coupler 230 l, 230 o or 240 l, 240 o.

Topology 200 a, 200 b may be laid out into an analog computer chip. Theanalog computer chip may be multi-layered. There may be at least twolayers of metal in the analog computer chip. Loops of superconductingmaterial 212 a-d may be laid out within a lower metal layer of theanalog computer chip. Loops of superconducting material 222 a-d may belaid out in an upper metal layer of the analog computer chip. Couplers230 a-p, 240 a-p may exist in both the upper metal layer and the lowermetal layer. Couplers 230 a-p, 240 a-p may exist in the upper metallayer when proximate to qubits 210 a-d and may exist in the lower metallayer when proximate to qubits 220 a-d. Vias may be used within couplers230 a-p, 240 a-p to bridge the upper metal layer and the lower metallayer.

Topology 200 a may be laid out in another multi-layered analog computerchip such that loops of superconducting material 212 a-d may be laid outwithin a lower metal layer, couplers 230 a-p, 240 a-p may exist in bothan upper and lower metal layer, and loops of superconducting material222 a-d may be laid out in both the upper metal layer and the lowermetal layer. Loops of superconducting material 220 a-d may existprimarily in the lower metal but may, through the use of vias, exist inthe upper metal layer when becoming proximate to loops ofsuperconducting material 210 a-d. There may exist additional metallayers which may be used for shielding within analog computer chips.

Examples of superconducting qubits include superconducting flux qubits,superconducting charge qubits, and the like. See e.g., Makhlin et al.,2001, Reviews of Modern Physics 73, pp. 357-400. Examples of flux qubitsthat may be used include rf-SQUIDs, which include a superconducting loopinterrupted by one Josephson junction, persistent current qubits, whichinclude a superconducting loop interrupted by three Josephson junctions,and the like. See e.g., Mooij et al., 1999, Science 285, 1036; andOrlando et al., 1999, Phys. Rev. B 60, 15398. Other examples ofsuperconducting qubits can be found, for example, in Il'ichev et al.,2003, Phys. Rev. Lett. 91, 097906; Blatter et al., 2001, Phys. Rev. B63, 174511, and Friedman et al., 2000, Nature 406, 43. In addition,hybrid charge-phase qubits may also be used.

In some embodiments quantum devices are flux qubits which are loops ofsuperconducting material. The actual shape of the loop is not important.This means that a roughly circular loop is no better or worse than anelongated “skinny” loop.

On-chip control circuitry may be laid out efficiently within areaswithin the grid defined by the qubits 210 and 220. Examples of on-chipcontrol circuitry can be found in U.S. Patent Application PublicationNo. 2008-0215850, U.S. patent application Ser. No. 12/109,847, U.S.patent application Ser. No. 12/120,354, and U.S. patent application Ser.No. 12/236,040.

Examples of interconnected topologies include U.S. Patent ApplicationPublication No. 2006-0225165, U.S. Patent Application Serial No.2008-0176750, and U.S. patent application Ser. No. 12/266,378.

Qubits 210, 220 interact. This is done by creating a mutual inductancebetween a qubit 210, 220 and coupler 230, 240. This mutual inductancetakes up significant physical space on the chip on which topology 200 a,200 b is laid, and a significant fraction of total qubit wire length.

Generally qubits with shorter and narrower wires increase the ratio ofinductance-to-capacitance (at a given β_(L)), where the ratio ofinductance-to-capacitance of a qubit determines the quantum levelspacing of the qubit. β_(L) may be defined as β_(L)=2πLI_(c) ^(l)/Φ₀,where L is the inductance of each respective qubit, I_(c) ^(l) is thecritical current of each respective qubit and Φ₀ is the magnetic fluxquantum. The further the levels are spaced, the more distinguishable thequantum effects exhibited by the qubit are. Processors with qubits thathave higher connectivity are considered more powerful (for a givennumber of qubits), but qubits with higher connectivities inherently havereduced quantum level spacings.

U.S. Patent Application Publication No. 2006-0225165 and U.S. patentapplication Ser. No. 12/266,378 use relatively small qubits and largecouplers. Analog and quantum processor topologies may use relativelylarge qubits and small couplers to produce quantum systems withincreased quantum effects. Each qubit may have a β_(L) (which isproportional to the inductance of the qubit multiplied by the criticalcurrent of the qubit) of about 3.5, whereas each coupler may have aβ_(L) between 1 and 1.5. At identical line widths and Josephson junctionsize, qubits should be about 3 times the physical size of couplers topromote quantum effects within analog processor topologies. Qubits maybe made larger by also increasing their line width thereby addingunneeded capacitance which decreases the qubit's ratio ofinductance-to-capacitance thereby reducing the quantum effects exhibitedby the qubit. Couplers can be made longer by the same means, whichtherein reduces their respective ratio of inductance-to-capacitance.

The present devices, systems and methods allow for qubits with shortpieces of wire and small Josephson junctions (translating to a largeinductance-to-capacitance ratio). Couplers are put wherever qubits crossor touch and extending couplers on top of the qubits for as long adistance as is needed may produce the desired mutual inductance andβ_(L) for couplers and qubits.

Ferromagnetic coupling implies that parallel fluxes are energeticallyfavorable and anti-ferromagnetic coupling implies that anti-parallelfluxes are energetically favorable. Examples of coupling devices can befound, for example, in U.S. Patent Application Publication No.2006-0147154, U.S. Patent Application Publication No. 2008-0238531, U.S.Patent Application Publication No. 2008-0274898, U.S. patent applicationSer. No. 12/238,147, and U.S. patent application Ser. No. 12/242,133.Alternatively, charge-based coupling devices may also be used.

FIG. 4 shows a fully connected K_(g) source graph 400 wherein each nodein the source graph is connected to every other node in the source graphby an edge. FIG. 5 shows a topology 500. Topology 500 includes threesubtopologies 501, 502, 503 where all subtopologies are similar totopology 200 a. Topology 500 may include subtopologies similar totopology 200 b.

Subtopologies 501, 503 may be used to embed two distinct K₄ graphs.Subtopology 502 may be used to encode a bipartite graph where abipartite graph is a graph whose vertices or nodes can be divided intotwo disjoint sets V₁ and V₂ such that every edge in the bipartite graphconnects a node in V₁ and a node in V₂; that is, there is no edgebetween two nodes in the same set. Subtopology 502 may embed a completebipartite graph such that there exists an edge between each node in V₁and each node in V₂, where each node in V₁ is associated with nodesembedded into subtopology 501 and each nodes in V₂ is associated withnodes embedded into subtopology 503.

Subtopology 501 may include qubits 510 a-d (collectively 510) and qubits520 a-d (collectively 520). Qubits 510 are laid out vertically andqubits 520 are laid out horizontally. Qubits 510, 520 may besuperconducting qubits. Each qubit 510 a-d may be a respective loop ofsuperconducting material interrupted by at least one respectiveJosephson junction. Each qubit 520 a-d may be a respective loop ofsuperconducting material interrupted by at least one respectiveJosephson junction. Couplers 530 a-530 p (collectively 530) couplequbits 510, 520. Each qubit 510 a-d is coupled to each qubit 520 a-dthrough four respective couplers from couplers 530. Each coupler 530 a-pmay be a respective loop of superconducting material. Each coupler 530a-p may be a respective loop of superconducting material interrupted byat least one respective Josephson junction.

Couplers 530 may mark the vertices of a grid defined by the qubits 510and 520 and exist where qubits 510, 520 are proximate to each otherthereby facilitating efficient coupling. By ferromagnetically couplingalong diagonal couplers 530 a, 530 f, 530 k, 530 p a fully connected K₄graph can be embedded into subtopology 501. In one embodiment, node 401may be embedded into qubits 510 a, 520 a where coupler 530 aferromagnetically couples qubits 510 a, 520 a together such that thestate of qubit 510 a is the same state as the state of qubit 520 a. Node402 may be embedded into qubits 510 b, 520 b where coupler 530 fferromagnetically couples qubits 510 b, 520 b together such that thestate of qubit 510 b is the same state as the state of qubit 520 b. Node403 may be embedded into qubits 510 c, 520 c where coupler 530 kferromagnetically couples qubits 510 c, 520 c together such that thestate of qubit 510 c is the same state as the state of qubit 520 c. Node404 may be embedded into qubits 510 d, 520 d where coupler 530 pferromagnetically couples qubits 510 d, 520 d together such that thestate of qubit 510 d is the same state as the state of qubit 520 d. Edge412 may be embedded into coupler 530 b, 530 e. Edge 413 may be embeddedinto coupler 530 c, 530 i. Edge 414 may be embedded into coupler 530 d,530 m. Edge 423 may be embedded into coupler 530 g, 530 j. Edge 424 maybe embedded into coupler 530 h, 530 n. Edge 434 may be embedded intocoupler 530 l, 530 o.

Subtopology 503 may include qubits 570 a-d (collectively 570) and qubits580 a-d (collectively 580). Qubits 570 are laid out vertically andqubits 580 are laid out horizontally. Qubits 570, 580 may besuperconducting qubits. Each qubit 570 a-d may be a respective loop ofsuperconducting material interrupted by at least one respectiveJosephson junction. Each qubit 580 a-d may be a respective loop ofsuperconducting material interrupted by at least one respectiveJosephson junction. Couplers 590 a-590 p (collectively 590) couplequbits 570, 580. Each qubit 570 a-d is coupled to each qubit 580 a-dthrough four respective couplers from couplers 590. Each coupler 590 a-pmay be a respective loop of superconducting material. Each coupler 590a-p may be a respective loop of superconducting material interrupted byat least one respective Josephson junction.

Couplers 590 may mark the vertices of a grid defined by the qubits 570and 580 and exist where qubits 570, 580 are proximate to each otherthereby facilitating efficient coupling. By ferromagnetically couplingalong diagonal couplers 590 a, 590 f, 590 k, 590 p a fully connected K₄graph can be embedded into subtopology 503. In one embodiment, node 405may be embedded into qubits 570 a, 580 a where coupler 590 aferromagnetically couples qubits 570 a, 580 a together such that thestate of qubit 570 a is the same state as the state of qubit 580 a. Node406 may be embedded into qubits 570 b, 580 b where coupler 590 fferromagnetically couples qubits 570 b, 580 b together such that thestate of qubit 570 b is the same state as the state of qubit 580 b. Node407 may be embedded into qubits 570 c, 580 c where coupler 590 kferromagnetically couples qubits 570 c, 580 c together such that thestate of qubit 570 c is the same state as the state of qubit 580 c. Node408 may be embedded into qubits 570 d, 580 d where coupler 590 pferromagnetically couples qubits 570 d, 580 d together such that thestate of qubit 570 d is the same state as the state of qubit 580 d. Edge456 may be embedded into coupler 590 b, 590 e. Edge 457 may be embeddedinto coupler 590 c, 590 i. Edge 458 may be embedded into coupler 590 d,590 m. Edge 467 may be embedded into coupler 590 g, 590 j. Edge 468 maybe embedded into coupler 590 h, 590 n. Edge 478 may be embedded intocoupler 590 l, 590 o.

Subtopology 502 may include qubits 540 a-d (collectively 540) and qubits550 a-d (collectively 550). Qubits 540 are laid out vertically andqubits 550 are laid out horizontally. Qubits 540, 550 may besuperconducting qubits. Each qubit 540 a-d may be a respective loop ofsuperconducting material interrupted by at least one respectiveJosephson junction. Each qubit 550 a-d may be a respective loop ofsuperconducting material interrupted by at least one respectiveJosephson junction. Couplers 560 a-560 p (collectively 560) couplequbits 540, 550. Each qubit 540 a-d is coupled to each qubit 550 a-dthrough four respective couplers from couplers 560. Each coupler 560 a-pmay be a respective loop of superconducting material. Each coupler 560a-p may be a respective loop of superconducting material interrupted byat least one respective Josephson junction. Each qubit 540 a-d may becoupled ferromagnetically or anti-ferromagnetically to a correspondingqubit from qubits 510 a-d such that qubit 510 a is coupled to 540 athereby embedding node 401 into qubit 540 a, qubit 510 b is coupled to540 b thereby embedding node 402 into qubit 540 b, qubit 510 c iscoupled to 540 c thereby embedding node 403 into qubit 540 c, and qubit510 d is coupled to 540 d thereby embedding node 404 into qubit 540 d.Each qubit 550 a-d may be coupled ferromagnetically oranti-ferromagnetically to a corresponding qubit from qubits 580 a-d suchthat qubit 580 a is coupled to 550 a thereby embedding node 405 intoqubit 550 a, qubit 580 b is coupled to 550 b thereby embedding node 406into qubit 550 b, qubit 580 c is coupled to 550 c thereby embedding node407 into qubit 550 c, and qubit 580 d is coupled to 550 d therebyembedding node 408 into qubit 550 d. Inter-subtopology coupling may beachieved with couplers 512, 523. Couplers 512 may be a series ofcoupling devices capable of coupling qubits 510 of subtopology 501 toqubits 540 of subtopology 502. Couplers 523 may be a series of couplingdevices capable of coupling qubits 550 of subtopology 502 to qubits 580of subtopology 503. Each coupler 512, 523 may be a respective loop ofsuperconducting material. Each coupler 512, 523 may be a respective loopof superconducting material interrupted by at least one respectiveJosephson junction.

There may exist inter-subtopology couplers which do not couple lineardistances between qubits two sub-topologies. Rather, there may existcorner couplers which couple together pairs of qubits of two differentsub-topologies which run perpendicular to one another, and the cornercoupler couples these two perpendicular qubits by having an about 90degree corner in the coupler length.

Couplers 560 may mark the vertices of a grid defined by the qubits 540and 550 and exist where qubits 540, 550 are proximate to each otherthereby facilitating efficient coupling. Edge 415 may be embedded intocoupler 560 a. Edge 425 may be embedded into coupler 560 b. Edge 435 maybe embedded into coupler 560 c. Edge 445 may be embedded into coupler560 d. Edge 416 may be embedded into coupler 560 e. Edge 426 may beembedded into coupler 560 f. Edge 436 may be embedded into coupler 560g. Edge 446 may be embedded into coupler 560 h. Edge 417 may be embeddedinto coupler 560 i. Edge 427 may be embedded into coupler 560 j. Edge437 may be embedded into coupler 560 k. Edge 447 may be embedded intocoupler 560 l. Edge 418 may be embedded into coupler 560 m. Edge 428 maybe embedded into coupler 560 n. Edge 438 may be embedded into coupler5600. Edge 448 may be embedded into coupler 560 p.

One may embed graphs with higher numbers of nodes by adding additionalK₄ and complete bipartite graphs to topology 500. By creating twotopologies 500 and a bipartite graph made of four subtopologies 503arranged in a 2×2 square, a complete K₁₆ graph may be embedded.

The graphs embedded into topologies 200 a, 200 b, 500 need not becomplete. Sparsely filed graphs may also be embedded into largertopologies.

FIG. 6 shows topology 600. Topology 600 comprises subtopologies 601,602, 603 in addition to subtopologies 501, 502, 503 from FIG. 5.Inter-subtopology couplers 511, 512, 523, 531, 533, 612, 623 may also belocated within topology 600. Subtopologies 501, 503 are coupled tosubtopologies 601, 603 through couplers 511, 531, 533 such that a 2×K₈graph can be embedded into topology 600. Each K₈ graph or portionthereof, such as source graph 400 of FIG. 4, may be coupled to variablesfrom the second K₈ graph. One K₈ graph may be embedded intosubtopologies 501, 502, 503 and a second K₈ graph may be embedded intosubtopologies 601, 602, 603. The couplers 511, 512, 523, 531, 533, 612,623 between qubits of subtopologies 501, 503 and subtopologies 601, 603may be controllable such that both ferromagnetic couplings,anti-ferromagnetic couplings, zero couplings and transverse couplingsmay be created between pairs of adjacent qubits.

Superconducting Probe Card

The various embodiments described herein provide systems and devices forsuperconducting probe cards. A superconducting probe card may include atleast one superconducting needle that is capable of establishing asuperconducting connection with a superconducting integrated circuit.While normal-metal and non-superconducting probe cards are well known inthe art (such as those sold by, for example, Wentworth Laboratories,Inc. of 500 Federal Road, Brookfield, Conn. 06804, USA), no previousdescription or implementation of a superconducting probe card are knownby the inventors.

In the operation of an integrated circuit such as integrated circuitsincorporating topologies such as those depicted schematically intopologies 200 a, 200 b, 500, 600, an interface to a separate system ofelectronics is typically established. Through such an interface, signalsmay be communicated to/from the integrated circuit for a variety ofpurposes, including but not limited to: power distribution,communication, system programming, calibration, measurements, systemmonitoring, circuit control, feedback, calculation, operation, and thelike. When communicating with the components of a superconductingintegrated circuit (“SIC”), it may be desirable to establish asuperconducting communication interface as opposed to anon-superconducting communication interface. A superconductingcommunication interface can be beneficial in some applications becauseit can reduce the heat load on the refrigeration system (required toreach superconducting temperatures) and it can reduce the level ofsignal noise being coupled to the SIC. This latter benefit may be ofparticular importance in applications involving highly sensitive SICs,such as superconducting processors and/or superconducting quantumprocessors.

The implementation of a superconducting interface for communicating witha SIC has been seen in the art. A common technique is to wire-bond tothe SIC using superconducting wire, such as aluminum wire. For furtherdetails of systems involving superconducting wire-bonding, see U.S.patent application Ser. No. 12/016,801.

While effective, manual wire-bonding is a slow and labor-intensiveprocess. The communication interface with a SIC may involve any numberof individual communication paths, and applications that include manysuch paths (i.e., on the order of a hundred or more) may take a longtime to manually wire-bond. Furthermore, wire-bonding is a process thatcannot be readily undone. As previously stated, in some applicationstesting, analysis and/or repair may be simplified if the SIC may beeasily removed from the system and/or substituted. The implementation ofa superconducting probe card allows superconducting connections to theSIC to be made quickly and easily, while still allowing the SIC to bereadily removed or replaced.

A probe card is a device designed to quickly provide a communicationinterface with an integrated circuit. Typical probe cards may include aprinted circuit board (PCB) that is communicably connected to aplurality of conductive needles extending therefrom. The conductiveneedles are arranged such that, when positioned adjacent to theintegrated circuit, respective needles of the probe card aligns with aparticular component or contact pad on the integrated circuit. The probecard needles may then collectively be brought in contact with thecorresponding components or contact pads of the integrated circuit,establishing communicative connections therebetween. Communicativeconnections may be maintained while the probe card needles remain incontact with corresponding components or contact pads of the integratedcircuit. Probe cards are presently available in a wide variety of forms;however, the various embodiments described herein represent the firstdescriptions of probe cards that are intended to provide superconductingconnections to a superconducting integrated circuit at cryogenictemperatures.

Tungsten-3% rhenium is a standard alloy that is typically used to formthe needles of a normal-metal probe card in applications requiringnon-superconducting connections. This material is often used, at leastin part, because it is ductile and durable. Durability is of particularimportance in a probe card needle because, in operation, the needle ispressed in firm contact against a component or contact pad in anintegrated circuit. Indeed, the pressure is such that the needle oftenscrapes away a portion of the contact pad. The needle must therefore bedurable to survive repeated use and ensure reliable contacts are made insuccessive uses.

The tungsten-3% rhenium alloy may be capable of superconducting, butonly at very low temperatures below 1K. However, as described inBlaugher et al., “The Superconductivity of Some IntermetallicCompounds”, IBM Journal (1962), pp. 117-118, the critical temperature ofthe alloy (that is, the temperature below which the alloy superconducts)increases as the proportion of rhenium increases up to about 40%. Thus,in accordance with the present systems and devices, a superconductingprobe card is described that employs needles formed of atungsten-rhenium alloy comprising a substantially greater proportion ofrhenium than previously used in the art. In some embodiments, an alloyof tungsten-26% rhenium is used to form the superconducting probe cardneedles.

A superconducting probe card may be specifically designed to operatearound at least one of two temperatures: a system-testing temperatureand a full-implementation temperature. Typically, a full-implementationtemperature is colder than a system-testing temperature. In systemtesting, the superconducting probe card may be used to test and analyzea SIC at a temperature that is below the critical temperature of the SICbut that is nevertheless above the temperature at which the SIC would beoperated if it was being fully-implemented. A reason for doing thiswould be to analyze and confirm the superconducting electrical behaviorof the SIC before committing the resources to cooling the SIC to thetemperature of full-implementation. For example, if the SIC includes asuperconducting processor, such as a superconducting quantum processor,then it may be desirable to test the SIC behavior in the superconductingregime before committing to cool the SIC to the milliKelvin environmentthat is desired for superconducting quantum computation. One of theeasiest and fastest ways to cool a device to the superconducting regimeis an immersion in a liquid coolant, such as liquid helium. A bath ofliquid helium-4 may maintain a temperature of ˜4.2K if stored in aninsulated dewar. 4.2K is below the critical temperature of somesuperconducting materials (e.g., lead and niobium) and thereforeprovides an adequate testing temperature for many SIC applications.Furthermore, a volume of liquid helium-4 may easily be further cooled byevaporative cooling (i.e., pumping helium vapor out of the dewar) to atemperature range of ˜1K, which is below the critical temperature ofmany other superconducting materials (e.g., tin and aluminum). Thus, thesuperconducting electrical behavior of a SIC may be readily tested bydipping the SIC in a (pumped, if necessary) bath of liquid helium-4.

A superconducting probe card that is implemented for system testing mayemploy at least one superconducting material that has a criticaltemperature that is above the base temperature of the refrigerationsystem in which testing is carried out. For example, a superconductingprobe card that is used in a bath of liquid helium-4 may employ at leastone superconducting material that has a critical temperature above thetemperature of the liquid helium-4. In accordance with the presentsystems and devices, a superconducting probe card may include needlesthat are formed of a material that is superconducting in the range ofabout 1K-5K. As shown in Blaugher et al., this corresponds to atungsten-rhenium alloy with about 10%-30% rhenium (i.e. tungsten-10%rhenium to tungsten-30% rhenium). Within this range, tungsten-26%rhenium is an alloy that is readily available in wire form because it iscommonly used in high-temperature thermocouple devices.

A superconducting probe card that is used when the system isfully-implemented may employ at least one superconducting material thathas a critical temperature that is above the base temperature of therefrigeration system employed for full implementation. For example, asuperconducting probe card that is used to provide a superconductingcommunication interface with a superconducting processor, such as asuperconducting quantum processor, may employ superconducting materialsthat have a critical temperature that is above the operation temperatureof the superconducting quantum processor. Typically, a superconductingquantum processor may be operated in the milliKelvin range, thus thesuperconducting probe card should employ superconducting materials thathave a critical temperature above this range. Note that the temperaturerange for system testing is typically higher than the temperature rangefor full-system implementation, therefore a superconducting probe cardthat is suitable for system testing temperatures may also be suitablefor full-system implementation temperatures, but not necessarily viceversa.

FIG. 7 shows a superconducting probe card 700 according to oneillustrated embodiment. Probe card 700 includes PCB 701, which in theillustrated embodiment includes four arms 701 a-701 d. Those of skill inthe art will appreciate that, in alternative embodiments, PCB 701 maytake on any form or geometry. Though not shown, PCB 701 may include aplurality of superconducting traces, each of which couples to arespective superconducting contact pad 711 a, 711 b (only two called outin FIG. 7, collectively 711). The superconducting traces (not shown) maybe formed directly by a superconducting material, or they may be formedby a non-superconducting material that is plated with a superconductingmaterial. Contact pads 711 may provide connection sites forsuperconducting needles 720 (only one called out in the Figure). PCB 701may also includes hole 730 through which superconducting needles 720 mayextend to establish superconducting communicative connections with asuperconducting device 740. In some embodiments, each of needles 720 maybe bent at some point along their respective lengths to extend throughhole 730.

The illustrated embodiment of probe card 700 is simplified, showingcontact pads 711 and needles 720 connected only to arm 701 a and similarstructures are not shown connected to arms 701 b-701 d. This has beendone with the intention of reducing clutter in FIG. 7, and those ofskill in the art will appreciate that arms 701 b-701 d may includesimilar structures and features as those illustrated and described forarm 701 a. For similar reasons, the superconducting traces on PCB 701have been omitted from FIG. 7. Those of skill in the art will appreciatethat such traces may be carried by any surface or portion of theinsulative material of PCB 701, including inner layers of the PCB 701,and may ultimately provide superconductingly communicative connectionsto a separate signal distribution system. Furthermore, the illustratedembodiment in FIG. 7 shows some needles as white and some needles asblack. In the illustration, black is used to denote needles that areconnected to ground on PCB 701 as opposed to respective contact pads711. However, those of skill in the art will appreciate the probe card700 may include any number of needles 720, and any corresponding numberof ground needles (shown in black), including embodiments with no groundneedles, as required by the application.

As previously described, superconducting needles 720 may be formed of asuperconducting material that has a critical temperature above theintended operating temperature of superconducting probe card 700. Anexample of such a material is an alloy of tungsten-rhenium, such astungsten-26% rhenium. A first end of each of superconducting needles 720is superconductingly communicably coupled to a respective contact pad711 on PCB 701. In some embodiments, this coupling is a fixed connectionrealized by, for example, a solder connection. A second end of each ofsuperconducting needles 720 is superconductingly communicably coupled toa respective contact pad 741 on superconducting device 740. In someembodiments, this coupling may be a free connection that is realized bydirect physical contact between each needle tip and a respective one ofcontact pads 741. Consequently, all of the needle tips may be aligned ina coplanar fashion in some embodiments, where the probe card 700 will beused with a superconducting device 740 that has a set of planar contactpads 741. In other embodiments, the needle tips may be aligned in anon-coplanar fashion, for example where the probe card 700 will be usedwith a superconducting device 740 that has a set of non-coplanar contactpads 741. In some embodiments, a first set of needle tips may lie in afirst plane and a second set of needle tips may lie in a second plane,different from the first plane. In some such embodiments, the first andthe second planes may be substantially parallel to one another.

Superconducting device 740 may take on a variety of forms and mayinclude a superconducting integrated circuit. In some embodiments,superconducting device 740 may include a superconducting processor, suchas a superconducting quantum processor. Such a superconducting quantumprocessor may include circuits which look similar to one of topology 200a, 200 b, 500, 600. In such embodiments, each of contact pads 741 may besuperconductingly communicably coupled to a respective device orcomponent of superconducting quantum processor 740. Examples of devicesor components that may be included in superconducting quantum processor740 include, but are not limited to: superconducting flux qubits,superconducting phase qubits, superconducting charge qubits,superconducting hybrid qubits, superconducting coupling devices,superconducting readout devices, and superconducting on-chip programmingdevices. Further details of superconducting on-chip programming devicesare provided in US Patent Publication 2008-215850.

As previously described, in some embodiments a first end of each ofneedles 720 may be superconductingly communicably coupled to arespective contact pad 711 on PCB 701 by a solder connection. However,an alloy of tungsten-rhenium is not readily solderable. In the art,tungsten-rhenium (of low rhenium composition) is often used innon-superconducting electrical applications and, when a solderconnection is desired, the tungsten-rhenium is plated with a layer ofnickel. However, nickel is not a superconducting material, thus in asuperconducting probe card such a nickel coating would interrupt thesuperconductivity of the signal. In accordance with the present systemsand devices, at least a portion of each of superconducting needles 720may be plated with a superconducting material that is solderable, suchas zinc.

FIG. 8A shows a superconducting needle 800 a for use in asuperconducting probe card, according to one illustrated embodiment. Aspreviously discussed, needle 800 a may be formed of a material that iscapable of superconducting at a temperature that is at or above theoperating temperature of the probe card. For example, needle 800 a maybe formed of an alloy of tungsten-rhenium, where the criticaltemperature of the alloy depends on the ratio of tungsten:rhenium in thealloy. Alloys of tungsten-rhenium are well-suited to be used as probecard needles because they are very hard and therefore less likely to bedamaged by repeated contacts with SICs. Indeed, alloys oftungsten-rhenium are already used in the art to form probe card needles;however, these applications (see, for example, publication of “ProbeNeedle Part Number Clarification, Terminology, Tolerances and MaterialProperties” provided by Point Technologies Inc. athttp://www.pointtech.com/pdf/def_mat_number.pdf) are limited tosemiconductor and non-superconducting applications. In accordance withthe present systems and devices, needle 800 a may be formed of an alloyof tungsten-rhenium that contains a greater proportion of rhenium thanpreviously implemented in the art, for the novel purpose of forming asuperconducting probe card.

Superconducting needle 800 a includes a main body or shaft 801 and atapered end 802 ending in a point or needle tip 810. Tapered end 802 isused to establish a physical and superconductingly electrical connectionwith a contact pad on a superconducting device, such as superconductingdevice 740 from FIG. 7. Somewhere along the length of shaft 801, andpreferably at or close to end 811, needle 800 a may be connected (e.g.,soldered) to a superconducting contact pad on the PCB portion of asuperconducting probe card. In order to facilitate this connection, atleast a portion of shaft 801 may be coated with a material that issuperconducting and also readily solderable. Zinc is an example of sucha material. In some embodiments, the zinc-plating is only used on shaft801 and not on tapered end 802 or point 810. This defines a border 803between zinc and tungsten-rhenium on the surface of needle 800 a. Thoseof skill in the art will appreciate that, in alternative embodiments,border 803 may be positioned at a different location relative to end811, point 810, and tapered end 802 than that shown in FIG. 8A. Those ofskill in the art will also appreciate that the relative lengths betweenshaft 801 and tapered end 802, as shown in FIG. 8A, may vary inalternative embodiments. Needle 800 a may be chemically etched tosimilar specifications as those used for tungsten-rhenium probe cardneedles for semiconductor and non-superconducting purposes. However, inaccordance with the present systems and devices the tungsten-rheniumalloy has a higher proportion of rhenium (e.g. tungsten-26% rhenium)such that the critical temperature of needle 800 a is higher than thatof typical semiconductor probe card needles.

As previously discussed, a superconducting probe card needle may includeat least one bend at some point along its length such that the tip ofthe needle extends through a hole (such as hole 730) in the probe cardPCB. FIG. 8B shows a superconducting needle 800 b for use in asuperconducting probe card, according to one illustrated embodiment.Needle 800 b is similar to needle 800 a from FIG. 8A, except that needle800 b includes a bend 820 in its length. Those of skill in the art willappreciate that the relative proportions of needle 800 b may vary indifferent embodiments. For instance, bend 820 may occur closer to end830 or closer to tip 831 as needed. Similarly, while bend 820 is shownas being approximately 90 degrees, those of skill in the art willappreciate that a bend of a different angle, either more or less than 90degrees, may be used in alternative embodiments. Furthermore, the border833 between zinc and tungsten-rhenium on the surface of needle 800 b mayoccur at a different position relative to bend 820 in variousembodiments. In some embodiments, needle 800 b may include a secondbend, similar to bend 820, proximate end 830 to facilitate contact witha specific conductive trace or contact pad on the probe card PCB.

Those of skill in the art will appreciate that the present systems anddevices may be implemented with a wide variety of probe card needledesigns, not just the probe card needle design illustrated in FIGS. 8Aand 8B. For example, the present systems and devices may be implementedusing blade probe card needles and/or Kelvin probe card needles.

As previously discussed, in known semiconductor and non-superconductingprobe card designs, the needles may be plated with nickel in order tofacilitate soldering. In accordance with the present systems and devicessuperconducting probe card needles may be plated with zinc as opposed tonickel to facilitate soldering. Zinc may be preferred to nickel in thedesign of a superconducting probe card because zinc is a superconductingmaterial while nickel is not. Furthermore, many applications ofsuperconducting electronics, such as superconducting quantumcomputation, may be particularly sensitive to magnetic fields. In suchapplications, it may be desirable to predominantly use materials thatare substantially non-magnetic. Both zinc and tungsten-rhenium alloysare substantially non-magnetic and suitable for use in a magneticallyquiet environment.

Those of skill in the art will appreciate that the superconducting probecard needles described in the present systems and devices may be platedwith an alternative superconducting and readily solderable material. Forexample, in some embodiments at least a portion of a superconductingprobe card needle may be plated with lead, tin, or an alloy of tin/lead.An alloy of tin/lead has a higher critical temperature than zinc, andfor this reason may be preferred in embodiments that are operated athigher cryogenic temperatures (e.g., liquid Helium-4 temperatures).Those of skill in the art will recognize that the critical temperatureof zinc is such that it may not be superconducting at liquid Helium-4temperatures. However, in such applications the thickness of the zinclayer may be on the order of a few microns, thereby providing aresistance that may be negligible in some applications.

A further aspect of the present systems and devices is the use of asuperconducting PCB in a superconducting probe card. A superconductingPCB, such as PCB 701 in FIG. 7, includes conductive traces that areformed by (or plated with) a superconducting material. Such traces areused as superconducting communication conduits connecting between thecontact pads 711 on the PCB 701 and some external signal distributionsystem. For example, in a system-testing implementation, thesuperconducting traces on PCB 701 may connect to an input/output systemof a dip probe that is used for fast testing of circuits in a bath ofliquid refrigerant. Alternatively, in a full-system implementation, thesuperconducting traces on PCB 701 may connect to superconductingcommunication conduits in a full-scale input/output system such as thatdescribed in U.S. patent application Ser. No. 12/016,801 and/or thatdescribed in U.S. patent application Ser. No. 12/256,332.

In some embodiments of the present systems and devices, at least twosuperconducting probe card needles may be superconductingly communicablycoupled to the same conductive trace or contact pad on thesuperconducting PCB. Such embodiments may be particularly suited forproviding communication conduits with multiple chips using a singleprobe card device. In such applications, each of the at least twosuperconducting probe card needles that are coupled to the sameconductive trace on the superconducting PCB may also besuperconductingly communicably coupled to a respective SIC.

The various embodiments described herein provide systems and devices fora superconducting probe card. A superconducting probe card can beadvantageous in applications involving testing of SICs, as well as inapplications involving full implementation of SICs. The probe cardapproach may be advantageous over other means of establishingcommunicative connections with an integrated circuit, such aswire-bonding, because connecting (and disconnecting) a probe card withan integrated circuit can be done very quickly. The superconductingprobe cards described herein provide a substantially non-magneticcommunicative interface with a SIC, where the communicative interfacemay include a plurality of communication conduits and each communicationconduit provides a substantially uninterrupted superconducting paththrough the probe card into and from the SIC.

Throughout this specification and the appended claims, the term“superconducting” when used to describe a physical structure such as a“superconducting needle” is used to indicate a material that is capableof behaving as a superconductor at an appropriate temperature. Asuperconducting material may not necessarily be acting as asuperconductor at all times in all embodiments of the present systemsand devices.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe embodiments to the precise forms disclosed. Although specificembodiments of and examples are described herein for illustrativepurposes, various equivalent modifications can be made without departingfrom the spirit and scope of the disclosure, as will be recognized bythose skilled in the relevant art. The teachings provided herein of thevarious embodiments can be applied to other analog processors, notnecessarily the exemplary quantum processors generally described above.

The various embodiments described above can be combined to providefurther embodiments. To the extent that they are not inconsistent withthe specific teachings and definitions herein, all of the U.S. patents,U.S. patent application publications, U.S. patent applications, referredto in this specification and/or listed in the Application Data Sheetincluding but not limited to U.S. Provisional Patent Application Ser.No. 61/039,041, filed Mar. 24, 2008 and entitled “Systems, Methods AndApparatus for a Superconducting Probe Card”, and U.S. Provisional PatentApplication Ser. No. 61/039,710 filed Mar. 26, 2008 and entitled“Systems, Devices, And Methods for Analog Processing,” and which areassigned to the assignee of this application are incorporated herein byreference, in their entirety. Aspects of the embodiments can bemodified, if necessary, to employ systems, circuits and concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A system, comprising: a first qubit; asecond qubit, wherein a portion of the first qubit crosses a portion ofthe second qubit substantially perpendicularly; and a coupler that has aperimeter and that provides a communicative coupling between the firstqubit and the second qubit, the coupler physically proximate to theportion of the first qubit that crosses the portion of the second qubit.2. The system of claim 1 wherein the perimeter of the 1 couplerencompasses at least a part of the portion of the first qubit thatcrosses the portion of the second qubit.
 3. The system of claim 1wherein the perimeter of the coupler encompasses a first portion of thefirst qubit that does not cross the second qubit and a second portion ofthe second qubit that does not cross the first qubit.
 4. The system ofclaim 1 wherein the perimeter of the coupler comprises a first arm thatextends substantially parallel to a length of the first qubit and asecond arm that extends substantially parallel to a length of the secondqubit.
 5. The system of claim 1 wherein the first qubit includes a firstqubit loop of superconducting material that is superconductive at acritical temperature and at least one Josephson junction, the secondqubit includes a second qubit loop of superconducting material that issuperconductive at a second temperature and at least one Josephsonjunction, and the coupler includes a coupling loop of superconductingmaterial that is superconductive at a critical temperature.
 6. Thesystem of claim 5 wherein the coupling loop is interrupted by at leastone Josephson junction.
 7. The system of claim 5 wherein the coupler ison a separate layer from the first and the second qubits.
 8. The systemof claim 5 wherein the coupler is on a same layer as one of the first orthe second qubits.
 9. The system of claim 1 wherein the coupler isoperable to at least one of ferromagnetically, anti-ferromagneticallyand transversely couple the first qubit and the second qubit.
 10. Amulti-layered computer chip, comprising: a first plurality N of qubitslaid out at least partially in a first metal layer; a second plurality Mof qubits laid out at least partially in a second metal layer; each ofthe qubits of the second plurality of qubits cross each of the qubits ofthe first plurality of qubits; and a first plurality N times M ofcoupling devices, each of the coupling devices proximate to where arespective pair of the qubits from the first and the second plurality ofqubits cross each other.
 11. The multi-layered computer chip of claim 10wherein at least of the coupling devices comprises a first arm extendingsubstantially parallel to a length of a qubit of the first plurality ofN qubits and a second arm extending substantially parallel to a length asecond qubit of the second plurality of M qubits.
 12. The multi-layeredcomputer chip of claim 10 wherein the plurality of coupling devices arelaid out at least partially in the second metal layer.
 13. Themulti-layered computer chip of claim 10 wherein M is equal to N.
 14. Themulti-layered computer chip of claim 10, further comprising: a metalshielding layer positioned to reduce magnetic noise around the qubitsand the couplers.
 15. The multi-layered computer chip of claim 10wherein the second plurality of qubits is laid out in both the secondmetal layer and the first metal layer and a plurality of vias providerespective current paths between the second and the first metal layers.16. The multi-layered computer chip of claim 10 wherein the plurality ofcoupling devices is laid out in both the second metal layer and thefirst metal layer and a plurality of vias provide respective currentpaths between the second and the first metal layers.
 17. Themulti-layered computer chip of claim 10 wherein the qubits of the firstplurality of qubits are arranged parallel to one another, the qubits ofthe second plurality of qubits are arranged parallel to one another, andthe qubits of the second plurality of qubits are arrangedperpendicularly with respect to the qubits of the first plurality ofqubits.
 18. The multi-layered computer chip of claim 10, furthercomprising: a superconducting probe card to establish an interfacebetween the multi-layered computer chip and a digital computer, thesuperconducting probe card comprising: a printed circuit board includinga dielectric medium that carries at least a first conductive trace,wherein the first conductive trace is formed by a material that issuperconducting below a critical temperature; and at least a firstconductive needle that is at least partially formed by a material thatis superconducting below a critical temperature, wherein a first end ofthe first conductive needle is communicably coupled to the firstconductive trace on the printed circuit board and a second end of thefirst conductive needle is tapered to form a point; wherein the criticaltemperature of the first conductive trace and the critical temperatureof the first conductive needle are both approximately equal to orgreater than an operating temperature of the superconducting probe card.19. The multi-layered computer chip of claim 10 wherein the qubits ofthe first plurality of qubits are arranged in a consecutive order from afirst to an n^(th) qubit, the qubits of the second plurality of qubitsare arranged in a consecutive order from a first qubit to an m^(th)qubit, the first qubit of the first plurality of qubits isferromagnetically coupled to the first qubit of the second plurality ofqubits, a second qubit of the first plurality of qubits isferromagnetically coupled to a second qubit of the second plurality ofqubits, a third qubit of the first plurality of qubits isferromagnetically coupled to a third qubit of the second plurality ofqubits, a fourth qubit of the first plurality of qubits isferromagnetically coupled to a fourth qubit of the second plurality ofqubits, the first qubit of the first plurality of qubits is controllablycoupleable to each of the second, the third and the fourth qubits of thesecond plurality of qubits, the second qubit of the first plurality ofqubits is controllably coupleable to each of the first, the third andthe fourth qubits of the second plurality of qubits, the third qubit ofthe first plurality of qubits is controllably coupleable to each of thefirst, the second, and the fourth qubits of the second plurality ofqubits, and the fourth qubit of the first plurality of qubits iscontrollably coupleable to each of the first, the second, and the thirdqubits of the second plurality of qubits to form a first K₄ block. 20.The multi-layered computer chip of claim 19, further comprising: a thirdplurality I of qubits laid out in a first metal layer; a fourthplurality J of qubits laid out at least partially in a second metallayer; each of the qubits of the second plurality of qubits cross eachof the qubits of the first plurality of qubits; a fifth plurality K ofqubits laid out in a first metal layer; a sixth plurality L of qubitslaid out at least partially in a second metal layer; each of the qubitsof the second plurality of qubits cross each of the qubits of the firstplurality of qubits; a second plurality I times J of coupling devices,each of the coupling devices of the second plurality of coupling devicesat least partially encompassing an area where a respective pair of thequbits from the third and the fourth plurality of qubits cross eachother, wherein the qubits of the third plurality of qubits are arrangedin a consecutive order from a first to an nth qubit, the qubits of thefourth plurality of qubits are arranged in a consecutive order from afirst qubit to an nth qubit, the first qubit of the third plurality ofqubits is controllably coupleable to each of the first, the second, thethird and the fourth qubits of the fourth plurality of qubits, thesecond qubit of the third plurality of qubits is controllably coupleableto each of the first, the second, the third and the fourth qubits of thefourth plurality of qubits, the third qubit of the third plurality ofqubits is controllably coupleable to each of the first, the second, thethird, and the fourth qubits of the fourth plurality of qubits, and thefourth qubit of the third plurality of qubits is controllably coupleableto each of the first, the second, the third, and the fourth qubits ofthe fourth plurality of qubits to form a first bipartite block; and athird plurality K times L of coupling devices, each of the couplingdevices of the second plurality of coupling devices at least partiallyencompassing an area where a respective pair of the qubits from thethird and the fourth plurality of qubits cross each other, wherein thequbits of the fifth plurality of qubits are arranged in a consecutiveorder from a first to an nth qubit, the qubits of the sixth plurality ofqubits are arranged in a consecutive order from a first qubit to an nthqubit, the first qubit of the fifth plurality of qubits isferromagnetically coupled to the first qubit of the sixth plurality ofqubits, a second qubit of the fifth plurality of qubits isferromagnetically coupled to a second qubit of the sixth plurality ofqubits, a third qubit of the fifth plurality of qubits isferromagnetically coupled to a third qubit of the sixth plurality ofqubits, a fourth qubit of the fifth plurality of qubits isferromagnetically coupled to a fourth qubit of the sixth plurality ofqubits, the first qubit of the fifth plurality of qubits is controllablycoupleable to each of the second, the third and the fourth qubits of thesixth plurality of qubits, the second qubit of the fifth plurality ofqubits is controllably coupleable to each of the first, the third andthe fourth qubits of the sixth plurality of qubits, the third qubit ofthe fifth plurality of qubits is controllably coupleable to each of thefirst, the second, and the fourth qubits of the sixth plurality ofqubits, and the fourth qubit of the fifth plurality of qubits iscontrollably coupleable to each of the first, the second, and the thirdqubits of the sixth plurality of qubits to form a second K₄ block, andwherein the qubits of the third plurality of qubits areferromagnetically coupled with respective ones of the qubits of thefirst plurality of qubits and wherein the qubits from the fourthplurality of qubits are ferromagnetically coupled with respective onesof the qubits of the sixth plurality of qubits to form a first K₈ block.21. The multi-layered computer chip of claim 20, further comprising: anadditional plurality of qubits and an additional plurality of couplersconfigured to form a second K₈ block, wherein at least one qubit fromthe first K₈ block is controllably coupled to at least one qubit fromthe second K₈ block.
 22. The multi-layered computer chip of claim 20wherein at least one of the couplers is a corner coupler that isoperable to couple at least one qubit from the first K₄ block to acorresponding respective qubit from the either the fifth or the sixthplurality of qubits.
 23. A system, comprising: a first qubit; a secondqubit, wherein a portion of the first qubit crosses a portion of thesecond qubit; and a coupler that has a perimeter and that provides acommunicative coupling between the first qubit and the second qubit, thecoupler physically proximate to the portion of the first qubit thatcrosses the portion of the second qubit, wherein the first qubitincludes a first qubit loop of superconducting material that issuperconductive at a critical temperature and at least one Josephsonjunction, the second qubit includes a second qubit loop ofsuperconducting material that is superconductive at a criticaltemperature and at least one Josephson junction, and the couplerincludes a coupling loop of superconducting material that issuperconductive at a critical temperature.
 24. The system of claim 23wherein the portion of the first qubit crosses the portion of the secondqubit substantially perpendicularly.
 25. The system of claim 23 whereinthe perimeter of the coupler encompasses at least a part of the portionof the first qubit that crosses the portion of the second qubit.
 26. Thesystem of claim 23 wherein the perimeter of the coupler encompasses afirst portion of the first qubit that does not cross the second qubitand a second portion of the second qubit that does not cross the firstqubit.
 27. The system of claim 23 wherein the perimeter of the couplercomprises a first arm that extends substantially parallel to a length ofthe first qubit and a second arm that extends substantially parallel toa length of the second qubit.
 28. The system of claim 23 wherein thecoupling loop is interrupted by at least one Josephson junction.
 29. Thesystem of claim 23 wherein the coupler is on a separate layer from thefirst and the second qubits.
 30. The system of claim 23 wherein thecoupler is on a same layer as one of the first or the second qubits. 31.The system of claim 23 wherein the coupler is operable to at least oneof ferromagnetically, anti-ferromagnetically and transversely couple thefirst qubit and the second qubit.